1. Field of the Invention
The present invention relates to an optical signal transmission system and an optical signal transmission device using the system. More particularly, it relates to an optical signal transmission system using single mode optical fibers (SMF) as transmission paths to realize advantageous optical signal transmissions at super high speed, and an optical signal transmission device using the system.
2. Description of the Related Art
No optical transmission system has achieved 10 Gb/s optical signal transmission or greater at super high speed using single mode optical fibers as transmission paths until now.
Especially, although experimental results of generating a sub-signal, determining normality of repeaters, and switching optical transmission paths needed for an optical transmission system have been reported, no system for practical use has been reported.
When the conventional system is employed for generating a sub-signal, determining normality of repeaters, and switching optical transmission paths, the following structure may be formed, for example:
In other words, it is assumed that a sub-signal is accumulated by electrically modulating a main signal. Alternatively, the different optical source from the main signal is used to realize a method for generating a sub-signal determining normality of repeaters, and switching optical transmission paths.
For electrical modulation of a main signal, however, there is a need for devising a frame structure of the main signal. Especially, when a 10 Gb/s main signal or greater is employed, modulation causes much technical troubles relative to super high speed operations in an electrical circuit. Alternatively, this causes problems, such that a circuit scale becomes larger, and further, the cost becomes larger when different optical sources are employed respectively for main and sub-signals.